Currently, when a substrate is going to be preliminarily detected, usually a worker takes down the substrate from a cabinet, and holds it at hand for detecting whether there is a defect on the substrate by eyes. However, during picking and placing the substrate, the worker needs to hold the substrate by hand all the time. Since the hands of the worker would inevitably move, especially with prolonged of time holding the substrate, the movements of the hands would be transferred to the substrate, resulting in larger unsteady movements of the substrate, which easily leads to a crack or damage of the substrate, and in turn generates the defects of the substrate during picking and placing the substrate.